Global Status: G1Global Status Last Reviewed: 28Apr2009Global Status Last Changed: 25Nov1996Rounded Global Status: G1 - Critically ImperiledReasons: Formerly widespread throughout the Cumberland and Tennessee River systems in Tennessee, Alabama, and Virginia, this species has become extremely rare throughout its present range with only three (possibly two) viable populations remaining. The species is declining at all extant sites apparently because of unmanageable threats, habitat degradation and population sizes below viability levels.Nation: United StatesNational Status: N1
(25Nov1996)

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for state or provincial information you may wish to contact the data steward
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United States

Alabama (SX), Kentucky (S1), Tennessee (S1), Virginia (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE, XN: Listed endangered, nonessential experimental population(14Jun1976)Comments on USESA: Listed Endangered throughout its range, except in the free-flowing reach of the Tennessee River from the base of Wilson Dam downstream to the backwaters of Pickwick Reservoir and the lower 5 RM of all tributaries to this reach in Colbert and Lauderdale Counties, Alabama. Here it is listed as an experimental, non-essential population. (USFWS, 2001).

The USFWS, in cooperation with the State of Tennessee and Conservation Fisheries, Inc., announced a final rule to reintroduce this species into its historical habitat in the free-flowing reach of the French Broad River below Douglas Dam to its confluence with the Holston River, Knox County Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (Federal Register, 12 September 2007). The proposed rule for this action was published on June 13, 2006.

Range Extent: 1000-5000 square km (about 400-2000 square miles)Range Extent Comments: This species is known from the Cumberland and Tennessee river systems in Tennessee and Virginia. It was once common throughout the Tennessee River system. It is currently known from the middle Cumberland River in Smith County, Tennessee; the Tennessee River in Meigs County, Tennessee; and in the upper Powell and Clinch rivers in Tennessee and Virginia (Parmalee and Bogan, 1998; Jones et al., 2004). In Alabama, it historically occurred in the Tennessee River downstream of Muscle Shoals but has not been reported in Alabama since the 1930s, thus it is likely extirpated; but current reintroduction efforts are underway (Mirarchi et al., 2004).

Number of Occurrences: 1 - 5Number of Occurrences Comments: A 1980 survey by Virginia Tech and TVA found nine occurrences in Virginia. Currently the dromedary is reduced to possibly three reproducing populations. Reproducing populations occur only in the upper Clinch (158 river km) and Powell Rivers (79 river km) in Tennessee and Virginia above Norris Reservoir (Jones et al., 2004; USFWS, 1984). Back in 1984, the population in the Tennessee River was considered extremely rare since only three live specimens had been found in the Chickamauga Reservoir below Watts Bar Dam (USFWS, 1984) but this site is likely extirpated. Jones et al. (2004) report that based on shells recovered from aboriginal sites, it was once one of the most abundant species in the Tennessee River. Apparently, it is declining at four remaining populations, only older individuals are found in Tennessee River.

Population Size: 1 - 1000 individuals Population Size Comments: At least prehistorically, Dromus dromas was one of the most abundant species in the Tennessee River. It is apparently declining or has been eliminated from the 3 or 4 remaining populations (likely fewer than 1000 individuals), with only older, non-reproducing, individuals found in the Tennessee River.

Number of Occurrences with Good Viability/Integrity: Very few (1-3) Viability/Integrity Comments: Barr et al. (1994) determined (based on 1981 survey data) that viable populations exist in the Powell River. Reproducing populations occur only in the upper Clinch (158 river km) and Powell Rivers (79 river km) in Tennessee and Virginia above Norris Reservoir (Jones et al., 2004; USFWS, 1984).

Overall Threat Impact: Very high - highOverall Threat Impact Comments: Impoundments, siltation and pollution leading to water quality and habitat deterioration inadequate sewage treatment, coal mining, oil and gas drilling and poor land-use practices. USFWS (1984) cites alteration and destruction of stream habitat due to impoundment of the Tennessee and Cumberland Rivers and tributaries for flood control, navigation, hydroelectric power production, and recreation as the single greatest factor contributing to this species' decline. A second factor that has severely affected this species is siltation. This is especially evident with this species as it requires clean, flowing water over stable, silt-free rubble, gravel, and sand shoals to prevent smothering. Also coal production in the Appalachian region has increased in the last few decades; which results in increased silt runoff. A third factor, although on a much broader scale, is the impact caused by various pollutants. Evidence of pollution and associated mussel disappearance in these areas dates back to Ortmann (1918).

Short-term Trend: Decline of 30-70%Short-term Trend Comments: USFWS (1984) reported extant populations in the Tennessee, Cumberland, Clinch, and Powell Rivers. Back in 1984, the population in the Tennessee River was considered extremely rare since only three live specimens had been found in the Chickamauga Reservoir below Watts Bar Dam (USFWS, 1984) but this site is likely extirpated. Bogan and Parmalee (1998) and Jones et al. (2004) report that based on shells recovered from aboriginal sites, it was once one of the most abundant species in the Tennessee River. Apparently, it is declining at four remaining populations, only older individuals are found in Tennessee River.

Long-term Trend: Decline of 70-90%Long-term Trend Comments: Bogan and Parmalee (1998) and Jones et al. (2004) report that based on shells recovered from aboriginal sites, it was once one of the most abundant species in the Tennessee River. Apparently declining at four remaining populations, only older individuals found in Tennessee River. Historically, this species was widespread in the Tennessee and Cumberland Rivers including major tributary streams, but has become increasingly rare throughout its range (USFWS, 1984) including the upper Elk (Isom et al., 1973). It once occurred across Alabama in the Tennessee River and some tributaries but was extirpated from Alabama during the early 1900s, although a reintroduction program is underway (Williams et al., 2008). Ortmann (1925) reported it from the Elk River in Alabama but no museum specimens are known.

Intrinsic Vulnerability: Unknown

Environmental Specificity: Narrow. Specialist or community with key requirements common. Environmental Specificity Comments: This species only occurs in clean, silt-free, flowing water and is sensitive to changes in water quality (domestic pollution and coal washing) and physical disruption (USFWS, 1984).

Other NatureServe Conservation Status Information

Inventory Needs: Define extent, number and viability in existing population.

Protection Needs: Continue Clinch Valley Bioreserve initiatives to improve water quality and land-use practices through variety of governmental and private partners. Listed Endangered throughout its range, except in the free-flowing reach of the Tennessee River from the base of Wilson Dam downstream to the backwaters of Pickwick Reservoir and the lower 5 RM of all tributaries to this reach in Colbert and Lauderdale Counties, Alabama (USFWS, 2001).

The USFWS, in cooperation with the State of Tennessee and Conservation Fisheries, Inc., proposes to reintroduce this species into its historical habitat in the free-flowing reach of the French Broad River below Douglas Dam to its confluence with the Holston River, Knox County Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (USFWS, 2006).

Distribution

Global Range:
(1000-5000 square km (about 400-2000 square miles))
This species is known from the Cumberland and Tennessee river systems in Tennessee and Virginia. It was once common throughout the Tennessee River system. It is currently known from the middle Cumberland River in Smith County, Tennessee; the Tennessee River in Meigs County, Tennessee; and in the upper Powell and Clinch rivers in Tennessee and Virginia (Parmalee and Bogan, 1998; Jones et al., 2004). In Alabama, it historically occurred in the Tennessee River downstream of Muscle Shoals but has not been reported in Alabama since the 1930s, thus it is likely extirpated; but current reintroduction efforts are underway (Mirarchi et al., 2004).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other
NatureServe Network databases and when they appear on NatureServe Explorer,
for state or provincial information you may wish to contact the data steward
in your jurisdiction to obtain the most current data.
Please refer to our Distribution Data Sources to find
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Basic Description: A freshwater mussel - dromedary pearlymussel.General Description: see USFWS (1984)Reproduction Comments: Females are gravid from October through May and contain 33 to 151 conglutinates/female thus the species is bradytictic. Conglutinates are contained only in water tubes of outer gills, and typically observed in all the water tubes from anterior to posterior portion of the gill. Conglutinates are released one at at a time from late March to late April. This species is one of a few mussels in Lampsilinae that produce modified conglutinates released through the suprabranchial cavity. The species is bradytictic, but females release conglutinates over a relatively short period of time once glochidia are mature (similar to many tachytictic or short-term brooders) (Jones et al., 2004).

Stewardship Overview: This species was listed as federally endangered in the U.S. in 1976 and a recovery plan was created (USFWS, 1984).

Listed Endangered throughout its range, except in the free-flowing reach of the Tennessee River from the base of Wilson Dam downstream to the backwaters of Pickwick Reservoir and the lower 5 RM of all tributaries to this reach in Colbert and Lauderdale Counties, Alabama (USFWS, 2001).

The USFWS, in cooperation with the State of Tennessee and Conservation Fisheries, Inc., proposes to reintroduce this species into its historical habitat in the free-flowing reach of the French Broad River below Douglas Dam to its confluence with the Holston River, Knox County Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (USFWS, 2006).Biological Research Needs: Biological and ecological studies to determine life history and population traits.

Population/Occurrence Delineation

Group Name: Freshwater Mussels

Use Class: Not applicable Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information. Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance. Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls. Separation Distance for Unsuitable Habitat: 2 kmSeparation Distance for Suitable Habitat: 10 kmAlternate Separation Procedure:NoneSeparation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence. Date: 18Oct2004 Author: Cordeiro, J. Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.

Gordon, M.E. and J.B. Layzer. 1989. Mussels (Bivalvia: Unionoidea) of the Cumberland River review of life histories and ecological relationships. U.S. Fish and Wildlife Service Biological Report, 89(15): 1-99.

Howard, A.D. 1915. Some exceptional cases of breeding among the Unionidae. The Nautilus 29:4-11.

Strayer, D.L. 1999a. Use of flow refuges by unionid mussels in rivers. Journal of the North American Benthological Society 18(4):468-476.

Strayer, D.L. and J. Ralley. 1993. Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia) including two rare species of Alasmidonta. Journal of the North American Benthological Society 12(3):247-258.

U.S. Fish and Wildlife Service (USFWS). 2001. Endangered and Threatened Wildlife and Plants; establishment of nonessential experimental population status for 16 freshwater mussels and 1 freshwater snail (Anthony's Riversnail) in the free-flowing reach of the Tennessee River below the Wilson Dam, Colbert and Lauderdale Counties, Alabama. Federal Register, 66(115): 32250-32264.

U.S. Fish and Wildlife Service (USFWS). 2006. Endangered and threatened wildlife and plants; establishment of nonessential experimental population status for 15 freshwater mussels, 1 freshwater snail, and 5 fishes in the lower French Broad River and in the lower Holston River, Tennessee; Proposed Rule. Federal Register, 71(113): 34195-34230.

Van der Schalie, H. 1938a. The naiad fauna of the Huron River in southeastern Michigan. Miscellaneous Publication of the Museum of Zoology, University of Michigan 40:7-78.

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